Transitional fossil

Critics of evolution consider a transitional fossil or missing link in the fossil record is a proposed, but as-yet undiscovered, intermediate form between two similar species. A fossil which is transitional between two species will typically have some features of both, and several features which are developed halfway between the two.

"Why then is not every geological formation and every stratum full of such intermediate links? [...] This, perhaps, is the most obvious and gravest objection which can be urged against my theory."

He attributed the perceived lack of transitional fossils to imperfections in the geologic record. Apologists claim that this problem has not been resolved since Darwin's time.

"First, despite all the increased knowledge of the rock record after so much drilling and exploration, many conventional geologists still see the rock record much as Darwin did: a record of long ages with lots of gaps. [1]"

"the only direct evidence acceptable would be the discovery of fossil remains of some intermediate creature between one species and another. [2]"

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Counter-Apologetics

The theory of evolution suggests that ALL life forms are "transitional forms". Therefore, all fossils are transitional fossils. Whether or not we know what they are the transition between does not affect that.

Given that the process of fossilisation is rare, we would not expect every species to appear in the fossil record. Gaps are no objection to evolution.

"Fossilization is a rare event to start with, and most fossils that do form have not been and will not be found. [3]"

A species can evolve into existence in an area where fossilisation is extremely rare and gradually expand its population into an area where fossilisation is relatively common. This would result in the apparent sudden appearance of a species. However, there is no real mystery to solve.

The claim that there are no transitional forms between the transitional forms we've already discovered. When a fossil is discovered that is an intermediate form, there are effectively two gaps rather than one. To insist that more transitional fossils must be found to fill these gaps is unreasonable and absurd because that would be far beyond what is necessary to illustrate a species transition. It is also an instance of moving the goalposts.

Fossil evidence supports common descent

New species are often discovered in the fossil record which supports of theory of common descent. The advance of scientific understanding leads to the God of the gaps, in which God is the explanation for a shrinking set of phenomena.

While particular cases of transitional species may not have been fossilised and therefore will never be found, there are countless examples of known transitional forms. For instance, fossils that definitively link two genuses, orders, and classes. Specific gaps that were previously cited by apologists have been filled by later discoveries. The following is a short list:

Archaeopteryx is an intermediate form between theropod dinosaurs and modern birds. It had teeth and claws like a dinosaur, and avian feathers like a modern bird, large wings but sideways shoulder joints, along with several features common to both.

Tiktaalik is an intermediate form between fish and amphibians. It had gills and scales like a fish, lungs and rib bones and a movable neck like an amphibian, and fish-like fins with limb bones and a fully functional wrist joint with simple fingers.

Orrorin tugenensis, Ardipithecus kadabba and ramidus, Australopithecus anamensis, afarensis, africanus, bahrelghazali, and garhi, Kenyanthropus platyops, Paranthropus aethiopicus, boisei, and robustus, Homo habilis, rudolfensis, ergaster, antecessor, cepranensis, and rhodesiensis, for most of which there have been found several fossils, represent the chain of successive transitions between Sahelanthropus tchadensis and Homo sapiens sapiens (modern humans).